Alterations of Neuropsychological Function and Cerebral Glucose Metabolism After Cardiac Surgery Are Not Related Only to Intraoperative Microembolic Events

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Background and PurposeHigh-intensity transient signals (HITS) during cardiac surgery are capable of causing encephalopathy and cognitive deficits. This study was undertaken to determine whether intraoperative HITS cause alterations of neuropsychological function (NPF) and/or cerebral glucose metabolism (CMR Glc), even in a low-risk patient group, and whether induced changes are interrelated.MethodsEighteen patients without signs of cerebrovascular disease underwent elective coronary artery bypass grafting (CABG), and two of these additionally underwent valve replacement in normothermia. Intraoperatively, HITS were recorded by means of transcranial Doppler ultrasonography (TCD). Perioperatively, NPF and CMR Glc were assessed using a standardized complex test battery and positron emission tomography with18 F-2-fluoro-2-deoxy-D-glucose (FDG-PET), respectively.ResultsIntraoperatively, the number of HITS ranged from 90 to 1710 per patient and hemisphere, more on the right side than on the left (P<.05). HITS occurred primarily during cardiopulmonary bypass (71.3%) and, to a lesser extent, during aortic manipulation (22.2%). Changes in global and regional CMR Glc between first (one day preoperatively) and second (8 to 12 days postoperatively) FDG-PET scans were mild. No correlations were found between the number of HITS, age of patient, duration of cardiac ischemia or cardiopulmonary bypass and the changes in CMR Glc. In patients with recorded HITS and a postoperative decrease of regional CMR Glc (n=11), the maximal decrease of rCMR Glc in each hemisphere below the individual global change of CMR Glc correlated with the number of HITS (r=-0.46, P<.05). Limitations in NPF occurred 8 to 12 days postoperatively, resolved within 3 months, and were not found to be correlated to the absolute number of HITS or changes in CMR Glc.ConclusionsHITS during cardiac surgery can cause alterations of both NPF and CMR Glc, even in a low-risk patient group. However, the number of HITS and changes in NPF and CMR Glc are not necessarily interrelated, which indicates that (1) the location of brain damage related to HITS is more important for the development of NPF than is the absolute number of HITS, and (2) factors in addition to HITS might contribute to surgery-related brain damage. (Stroke. 1998;29:660-667.)

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